1. Field of the Invention
The present invention generally relates to a toner replenishment control for an image forming apparatus such as a copier, a facsimile machine, a printer or the like, in which a latent-image pattern is formed on an image carrying body, the development characteristic is measured from electric potential information thereof and a toner adhesion amount, and, from the development characteristic, various electric potentials at a time of forming images regularly are determined.
2. Description of the Related Art
In an image forming apparatus such as a copier, a facsimile machine, a printer, or the like, employing an electrostatic photographic method, generally speaking, a photosensitive body drum is rotated by a motor or the like, the photosensitive body drum is uniformly charged by a charging device, then, an electrostatic latent image is formed on the drum as a result of an image being written thereonto through image exposure thereof by an exposure device, the thus-formed electrostatic latent image is developed by a developing device so as to be a toner image, the toner image is then transferred to a transfer material by a transfer device, and the toner image is fixed onto the transfer material by a fixing device.
In the image forming apparatus which forms an image through the above-mentioned electrostatic photographic process, an electrostatic-latent-image electric potential of a test pattern of the electrostatic latent image formed on the photosensitive drum body is measured, the development characteristic is obtained from the toner adhesion amount of the above-mentioned test pattern visualized by toner, and, from this development characteristic, various electric potentials such as a development bias potential and a charging electric potential of the image carrying body (photosensitive body drum) are calculated.
For example, the electrostatic-latent-image electric potential of the test pattern of the electrostatic latent image is measured, the toner adhesion amount of this test pattern of electrostatic latent image visualized by toner is measured, and, then, by using the thus-obtained measurement data, a straight-line approximated formula of the development characteristic, that is, a development xcex3 characteristic, is obtained through straight-line approximation. Then, an inclination of this straight-line approximated formula is assumed as being a development efficiency, and, from the development efficiency, the various electric potentials to be used for regular image formation are obtained.
Further, in a normal (regular) image forming occasion, a toner detecting pattern (test pattern) for toner replenishment control is produced every predetermined number of sheets of printing, and a toner replenishment amount is calculated from the detection result of the toner adhesion amount of this toner detecting pattern. For example, the toner detecting pattern is produced in a predetermined image production condition, the detection value of the toner adhesion amount of the toner detecting pattern is compared with a toner replenishment control target value, and, based on this comparison result, a toner amount to be supplied (toner replenishment amount) is determined.
Further, according to the above-mentioned detection result of the (toner) development characteristic, a development potential for producing the above-mentioned toner detecting pattern is lowered when the above-mentioned detection result of the development characteristic is such that the developing performance is judged as being low. As a result, toner adhesion of the toner detecting pattern is made to be such that the toner adhesion is lower than the above-mentioned toner replenishment control target value for the toner detecting pattern, and, thereby, toner replenishment becomes more likely to be actually performed as a result of xe2x80x98toner lowxe2x80x99 being detected from the thus-intentionally-lowed toner adhesion of the toner detecting pattern. Thus, restoring of the development performance becomes more likely to be achieved.
However, in the above-described toner replenishment control method, when the development potential for producing the toner detecting pattern for toner replenishment control is altered, a resulting change in toner adhesion amount of the toner detecting pattern may vary according to a characteristic of the used developing agent, mechanical characteristic of the developing device, or environmental conditions. As a result, the toner adhesion amount of the toner detecting pattern may become excessively smaller or larger than an expected value.
In a case where toner replenishment control is performed based on a detection result of toner adhesion amount of the toner detecting pattern in a condition in which the toner detecting pattern is produced by fixed image production conditions, the toner replenishment control is performed such that the toner adhesion amount, in other words, the image density may not vary. However, the image production conditions may be intentionally altered for various reasons.
For example, there is a case where the developing potential is intentionally altered in order to change the toner adhesion amount of the toner detecting pattern so as to change the development performance. Further, in a system in which the image production conditions for the toner detecting pattern are made equal to be the image production conditions for regular image formation (in regular printing operation), the image production conditions for the toner detecting pattern are necessarily altered when the image production conditions for regular image formation are intentionally altered.
In such a case, the thus-altered image production conditions for the toner detecting pattern may result in change in the toner adhesion amount of the toner detecting pattern. However, the amount of change in the toner adhesion amount of the toner detecting pattern may not necessarily become an expected one.
For example, in a case where the toner density is to be increased because the detected development xcex3 characteristic is low, the development bias for developing the toner detecting pattern is intentionally lowed by 10 volts so that the development potential is lowered. Then, although the toner replenishment control target value has been equal to the toner adhesion amount of the toner detecting pattern immediately before the change, the toner adhesion amount of the toner detecting pattern may be reduced by an amount more than an expected one. In such a case, toner replenishment is automatically performed until the resulting toner adhesion amount becomes the toner replenishment control target value. For this purpose, the development performance may be excessively increased, and, this may result in undesired variation in density, and/or variation in color of printed images.
Such a problem may occur not only due to the above-mentioned fact that change in toner adhesion amount of the toner detecting pattern resulting from alternation of the development potential may differ due to environmental condition or the like, but also due to variation in the above-mentioned straight-line approximation for the development xcex3 characteristic, bad influence of a degraded control accuracy in a case where the development bias, charging electric potential, or exposure electric potential is made shifted, or the like.
Further, assuming that the toner detecting pattern for toner replenishment control is developed by a fixed development potential, the problem concerning shift of toner adhesion amount occurring by alteration of the development potential is reduced. However, when the charging characteristic of the developing agent varies due to aging and/or environmental variation, toner replenishment control is performed such that the developing amount may be made uniform with respect to the same potential. As a result, the toner density of the developing agent may vary too much, and, thereby, toner scattering, toner sticking, overflow of the developing agent, or the like may occur.
Thus, according to the toner replenishment control system in the related art, especially in a case where this is employed in a full-color copier which is likely affected by its development performance, undesired color variation may occur due to change in development performance. Especially, stability in highlight part of a resulting full-color image may be degraded.
An object of the present invention is to provide a toner replenishment control system by which the above-mentioned problems are solved, and, thereby, stable image density of a printed image can be maintained.
A toner replenishment control for an image forming apparatus comprising:
a) determining a second image production condition for a second toner detecting pattern based on a detection result of a toner adhesion amount of a first toner detecting pattern formed on an image carrying body according to a first image production condition;
b) performing toner replenishment control based on a detection result of a toner adhesion amount of the second toner detecting pattern formed by the second image production condition determined as mentioned above, and a toner replenishment control target value; and
c) altering the toner replenishment control target value to be used above based on the detection result of the second toner detecting pattern formed according to the second image production condition.
Thereby, when the image production condition is intentionally altered, the toner replenishment control target value is renewed based on a detection result of a toner adhesion amount of a toner detecting pattern formed according to the thus-altered image production condition. Accordingly, it is possible to effectively prevent an excessively large or excessively small control amount in toner replenishment control from being adopted. Thereby, it is possible to maintain an image density of printed image even through repetitive operations of toner replenishment control.
The above-described control process may further include correcting the above-mentioned alteration of the toner replenishment control target value, based on a current development performance (xcex3 performance/characteristic).
Thereby, it is possible to determine the toner replenishment control target value such that the toner replenishment amount may be increased as the development xcex3 performance becomes lower, and, also, the toner replenishment amount may be decreased as the development xcex3 performance becomes higher. As a result, the toner density in image development is properly adjusted, and, thus, it is possible to maintain a stable image density (printed image density) even over long operation of the image forming apparatus.
In the above-described control process, the toner replenishment control target value may be determined to be within a range in which a toner adhesion sensor for detecting for the first and second toner detecting patterns can have a proper sensitivity.
Thereby, it is possible to prevent the toner replenishment control from having run away due to occurrence of a possible extreme value of toner replenishment control target value. Accordingly, it is possible to perform high-reliability toner replenishment control.
In the above-described control process, the image production condition for the second toner detecting pattern may be the same as an image production condition for regular image formation performed.
Thereby, there is no necessity to perform complicated control such as switching of a charging bias, development bias, and so forth, especially for producing an image of the toner detecting pattern. Also, the toner detecting pattern may be made smaller. Accordingly, the toner consumption can be effectively reduced, and, high efficiency can be achieved in image formation.
Other objects and further features of the present invention will become more apparent from the following detailed description when read in conjunction with the accompanying drawings.